Fluid pressure actuated spring brake cylinders have been used on railway-type vehicles for a number of years. Generally, in the spring brake cylinders used prior to the present invention, the pot-shaped cylinder of the spring actuator portion is designed as a single piece with the cylinder base. See, for example, German Patent DE-PS No. 2943763. In this spring brake cylinder, a flange, which is located opposite the base, is detachably connected to the cylinder. This flange member serves the dual purpose of sealing the pressure chamber of the spring brake cylinder against the atmosphere and axially guiding the spring brake piston. The side of the flange member that is opposite the spring brake cylinder contains a service brake cylinder.
This prior art type spring brake cylinder is assembled by first placing a helical coil compression spring, which serves as the spring brake actuator, on the cylinder base. Subsequently, the spring brake piston is inserted into the cylinder with the assistance of a specially designed mounting device. The spring brake piston is moved toward the spring actuator until a mechanical brake release device, a portion of which is located outside of the cylinder base, can be mounted. The mechanical brake release device includes a screw bolt and a threaded disk. During assembly, the brake release device is used to pretension the spring brake piston at a predetermined position against the spring actuator so that the mounting device can be safely removed and the cylinder can then be connected to the flange member. When the brake release device is then loosened, the force of the released spring actuator moves the spring brake into an operating position. In this operating position, it can execute a working stroke when opened to fluid pressure.
During disassembly, the spring brake cylinder is dismantled by first separating the cylinder from the flange. Subsequently, the special mounting device is used to move the spring brake piston toward the spring actuator until the mechanical brake release device can be removed. The mounting device is then slowly relieved so that the force of the released spring actuator pushes the spring brake piston out of the cylinder.
As is evident from the above description, both the assembly and the disassembly process require a sequence of mounting steps. Therefore, they are relatively expensive and clearly not optimum with respect to the amount of time required for such assembly or disassembly. This is because the spring brake cylinder can only be maneuvered in the way described above by the special mounting device possessing the capability of pretensioning the spring actuator and holding it securely in place in its pretensioned position.
Another spring brake cylinder, which is also known in the art from German Patent DE-PS 1680232, has a base which is connected to the spring brake cylinder by an axial locking ring. In this arrangement, the axial locking ring can be detached from the assembly. This then allows the base, the spring actuator and the spring brake piston to be joined into one preassembled unit. During the assembly process, the spring brake piston can be pretensioned against the spring actuator through the assistance of the brake release device. After assembly, this unit can be inserted into the spring brake cylinder where it is then connected to such spring brake cylinder by way of the base and the axial locking ring. In this assembly, when the brake release device is subsequently loosened, the spring brake cylinder becomes operational in the manner described above.
A spring brake cylinder of this particular design, in which the base can be separated from the cylinder, requires the use of reinforced cylinder walls, at least in the area of the mounting for the axial locking ring. It should therefore be evident to those persons skilled in the braking art that a cylinder designed as a plate pulling part of light weight construction, which is highly desirable, cannot be achieved.
This particular spring brake cylinder arrangement includes an additional significant disadvantage in that, should the axial locking ring be loosened either inadvertently, or if inappropriately tightened initially while the spring brake cylinder is in an operative state, a sudden and uncontrolled release of the spring actuator will cause the unit, consisting of the base, spring actuator, spring brake piston and the brake release device, to be propelled out of the spring brake cylinder like a bullet. Therefore, to prevent this occurrence, both the assembly and the disassembly processes for this spring brake cylinder require the strict adherence to of rigid shop-based safety precautions which add substantially to the manufacturing cost of the spring brake cylinder. Even with the added precautions, it is not always possible to eliminate human error.